Catutthajhānapañhāsutta 
Catutthajhānapañhāsutta → upekkhāsuttaṁ (bj); upekkhako (pts1ed) A Question About the Fourth Absorption

“‘Catutthaṁ jhānaṁ, catutthaṁ jhānan’ti vuccati.  “They speak of this thing called the ‘fourth absorption’.
Katamaṁ nu kho catutthaṁ jhānanti?  What is the fourth absorption?
Tassa mayhaṁ, āvuso, etadahosi:  It occurred to me:
‘idha bhikkhu sukhassa ca pahānā dukkhassa ca pahānā pubbeva somanassadomanassānaṁ atthaṅgamā adukkhamasukhaṁ upekkhāsatipārisuddhiṁ catutthaṁ jhānaṁ upasampajja viharati.  ‘It’s when, giving up pleasure and pain, and ending former happiness and sadness, a mendicant enters and remains in the fourth absorption, without pleasure or pain, with pure equanimity and mindfulness.
Idaṁ vuccati catutthaṁ jhānan’ti.  This is called the fourth absorption.’

So khvāhaṁ, āvuso, sukhassa ca pahānā dukkhassa ca pahānā pubbeva somanassadomanassānaṁ atthaṅgamā adukkhamasukhaṁ upekkhāsatipārisuddhiṁ catutthaṁ jhānaṁ upasampajja viharāmi.  And so … I was entering and remaining in the fourth absorption.
Tassa mayhaṁ, āvuso, iminā vihārena viharato sukhasahagatā saññāmanasikārā samudācaranti.  While I was in that meditation, perception and focus accompanied by pleasure beset me.

Atha kho maṁ, āvuso, bhagavā iddhiyā upasaṅkamitvā etadavoca:  Then the Buddha came up to me with his psychic power and said,
‘moggallāna, moggallāna.  ‘Moggallāna, Moggallāna!
Mā, brāhmaṇa, catutthaṁ jhānaṁ pamādo, catutthe jhāne cittaṁ saṇṭhapehi, catutthe jhāne cittaṁ ekodiṁ karohi, catutthe jhāne cittaṁ samādahā’ti.  Don’t neglect the fourth absorption, brahmin! Settle your mind in the fourth absorption; unify your mind and immerse it in the fourth absorption.’

So khvāhaṁ, āvuso, aparena samayena sukhassa ca pahānā dukkhassa ca pahānā pubbeva somanassadomanassānaṁ atthaṅgamā adukkhamasukhaṁ upekkhāsatipārisuddhiṁ catutthaṁ jhānaṁ upasampajja vihāsiṁ.  And so, after some time … I entered and remained in the fourth absorption.

Yañhi taṁ, āvuso, sammā vadamāno vadeyya …pe… mahābhiññataṁ patto”ti.  So if anyone should be rightly called a disciple who attained to great direct knowledge with help from the Teacher, it’s me.”

Catutthaṁ.